MiniCalc is a program that resides in your system tray. By clicking on the tray icon or pressing Control+Shift+C, a small box will show up next to your mouse cursor where you can type various mathematical expressions.

It supports the pi and e constants, as well as trig functions.

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Press enter to compute your expression.

Press the up arrow to access your last computed expression.

Press escape to hide the input box.

Type "autocopy" in the box and hit enter if you want every answer to be copied to the clipboard automatically.

To exit, just right-click the tray icon.